<!doctype HTML>
<style>
  #target .child::before {
    content: "";
    position: absolute;
    height: 30px;
    width: 30px;
    will-change: transform;
    background-color: green;
  }
  #target.Slider_pressed .child::before {
    transform: translateZ(0);
    }
</style>
<div class="ContextualPopup" style="opacity: 0.9">
  <div id=target tabindex="-1" >
    <div class=child></div>
  </div>
  <div style="position: relative; z-index: 0">
    <div style=" position: absolute; z-index: -1; will-change: transform;"></div>
  </div>
<div style="position: absolute; height: 30px; width: 30px; left: 100px; background-color: green;">
</div>
